Attachment system and method for thermal protection system

ABSTRACT

An attachment system for mounting a tile of a thermal protection system to a substructure comprises a post assembly configured to interconnect the tile to the substructure. The post assembly is configured to allow relative sliding movement between the tile and the substructure along a plane which is generally parallel to the tile. The attachment system facilitates installation and removal of the tile from the substructure for inspection, maintenance and repair of the tile and/or the substructure.

CROSS-REFERENCE TO RELATED APPLICATIONS

(Not Applicable)

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

(Not Applicable)

FIELD

The present disclosure relates generally to thermal protection systems(TPS) and, more particularly, to a uniquely configured attachment systemfor mechanically attaching individual tiles to a substructure.

BACKGROUND

Thermal protection systems (TPS) are widely used on reusable launchvehicles (RLV's) such as the Space Shuttle to provide a thermal shieldagainst the very high temperatures of vehicle re-entry into the Earth'satmosphere. TPS may additionally be required on certain air vehiclessuch as hypersonic vehicles intended primarily for atmospheric flight.For example, TPS may be applied to portions of the air vehicle that aredownstream of jet engine exhaust or rocket engine exhaust. Such airvehicles may include fixed structure or control surfaces that arelocated within the exhaust plume and which are therefore subjected tothe extreme heat of such exhaust.

Future air and space vehicles to which TPS may be applied include crewexploration vehicles (CEV's) which may utilize modular architecture totransfer crew and cargo to the International Space Station and todestinations beyond. Other vehicles utilizing TPS may include vehicleshaving advanced air-breathing stages as well as supersonic air launchplatforms combining air-breathing and rocket stages for transatmosphericor orbital missions.

As applied to RLV's, TPS must be capable of surviving extremetemperatures ranging from −300° F. on orbit to up to 3,000° F. uponre-entry into the Earth's atmosphere. Regarding its thermally insulativecapabilities, TPS must be capable of maintaining the temperature ofmetallic or composite substructure below the temperature at which themechanical properties of the substructure may begin to degrade. Inaddition to protecting the vehicle substructure against extremetemperatures, TPS must also accommodate flight-induced deflections ofthe vehicle substructure. For example, TPS must be capable of adjustingto relative movement of the substructure under high strain conditions ofwing bending. In this regard, the attachment of TPS to the substructuremust be of sufficient flexibility under high structural strain.

Prior art TPS for re-entry vehicles such as the Space Shuttle comprise alarge number of insulative tiles formulated and/or sized for a varietyof substructure material compositions. The tiles are positioned atstrategic locations on the vehicle dependent upon the temperaturesoccurring at those locations. Current attachment technology for mountingTPS tiles to a substructure includes adhesive bonding. In one prior artattachment system, tiles may be first bonded to a strain isolation pad(SIP) which may be comprised of felt-like material. The SIP allows thetile to withstand flexing of the vehicle substructure under load. TheSIP may also accommodate thermal growth of the tile and may compensatefor acoustic excitation (i.e., vibration) during ascent to orbit.Following bonding to the tile, the SIP may be bonded to the substructureusing a thin layer of silicone adhesive.

Although prior art systems for attaching TPS are generally effective fortheir intended purposes, they possess certain drawbacks which detractfrom their overall utility. More specifically, the installation of tilesusing current attachment technology is extremely labor intensive andtime-consuming. For example, high-temperature reusable surfaceinsulation (HRSI) tiles are mounted on upper forward fuselage areas ofthe Space Shuttle and around certain portions of orbital maneuveringsystems (OMS) and reaction control system (RCS) pods of the Shuttle.

The HRSI tiles are first bonded to an SIP which, in turn, is bonded tothe Space Shuttle substructure using room temperature vulcanization(RTV) silicone adhesive. The RTV adhesive is applied to the substructurein thin layers of less than 0.010 inch. During the curing process, thetile/SIP may be forced against the substructure under pressure using avacuum bag which is sealed against the substructure to enclose an areawhere the tiles are to be bonded. Replacement of the tile includesremoval of old RTV followed by surface preparation of the substructureand then bonding and curing of a new tile element using the processdescribed above. The total process is rather lengthy and can entail asignificant amount of touch labor and vehicle down time.

A further drawback associated with current attachment technology for TPStiles is that the RTV silicone bond line is limited to 500° F.continuous operation temperature. Unfortunately, this temperaturelimitation necessitates the use of extremely expensive polyimidestructures directly under the TPS tiles in order to withstand the 500°F. operation temperature. An additional drawback associated with currentattachment technology is related to the inability to inspect thesilicone bond line after a tile is installed in order to verify bondquality. Also, current attachment technology of TPS tiles prevents quickaccess to underlying subsystems and structure for inspection,maintenance and servicing.

In order to improve the feasibility of hypersonic aircraft and futurespace vehicles, it is necessary to reduce the cost and time required toinstall TPS on such vehicles and to reduce the time required to inspect,remove, repair and replace tiles and underlying substructure. As can beseen, there exists a need in the art for an attachment system for TPSwhich facilitates rapid inspection of installed tiles and which allowsfor rapid access to underlying subsystems and structure for maintenanceand inspection. Additionally, there exists a need in the art for anattachment system for TPS which allows for rapid replacement of damagedtiles and which facilitates relative movement between the tiles andsubstructure at operating temperatures in order to prevent failure ofthe connection between the tile and the substructure.

Furthermore, there exists a need in the art for an attachment system forTPS which allows for the use of low cost, low operating-temperatureepoxy composite structures under the TPS in certain locations as opposedto the more expensive polyimide structures currently required to handlethe 500° F. operating temperatures. In this regard, there exists a needin the art for an attachment technology for TPS which provides arelatively large cooling channel between the tile and the exterior ofthe substructure (i.e., air vehicle or space vehicle) skin in order toimprove cooling capacity and permit operation at much highertemperatures. Finally, there exists a need in the art for an attachmentsystem for TPS which reduces vehicle down time to repair or replace adamaged tile.

BRIEF SUMMARY

The above described needs associated with thermal protection systems(TPS) are specifically addressed and alleviated by the variousembodiments disclosed herein. More specifically, a mechanical attachmentsystem is provided for removably mounting a tile of a thermal protectionsystem to a vehicle substructure. The attachment system includes atleast one post assembly for mounting at least one tile in spacedrelation to a substructure such that a cooling gap is formed between thetile and the substructure. The post assembly is specifically configuredto facilitate sliding movement of the tile relative to the substructurealong a plane that is generally parallel to the tile for structuraladvantages.

The technical effects of the embodiments disclosed herein include theability to facilitate relative sliding movement between the tile and thesubstructure in at least one of first and second sliding directionswherein the first sliding direction is preferably, but optionally,perpendicular to the second sliding direction. In addition, the postassembly is sized and configured to locate the installed tiles in spacedrelation to the substructure to provide a channel for the flow ofcooling air to increase operating temperatures.

In one embodiment, the attachment system comprises the post assembly toremovably secure the tile to the substructure. The post assembly maycomprise a lower element, a center element and an upper element. Thelower element may be fixedly mountable to the substructure such as bybonding with a suitable film adhesive such as silicone or polyimideadhesive or other high-temperature adhesive. The center element may beslidably engageable to the lower element. The upper element may befixedly mountable to the tile and may be slidably engageable to thecenter element. In this regard, the upper element is preferably slidablerelative to the center element along the first sliding direction. Thecenter element is preferably slidable relative to the lower elementalong the second sliding direction.

However, it is contemplated that the post assembly may be configured tofacilitate relative movement in a plane generally parallel to the tilebut in only a single sliding direction or in three or more slidingdirections. In addition, the post assembly may be configured tofacilitate relative movement in sliding directions that are oriented innon-perpendicular relationship to one another. For example, it iscontemplated that the post assembly may be configured to allow forrelative sliding movement along first, second and third slidingdirections which are each oriented at 60 degree angles relative to oneanother.

The attachment system may comprise a strain isolation pad (SIP) which ispreferably disposed between the post assembly and the tile in order toallow the tile to move slightly relative to the substructure withoutcompromising the strength of the joint therebetween. The SIP may alsoisolate the tile from structural deflections of the vehicle as well asfrom thermal expansion and acoustic excitation as a means to reducestress in the tile.

The attachment system may comprise an interlocking mechanism such as,without limitation, a tongue and groove arrangement disposed between atleast one of the upper, center and lower elements. For example, thecenter element may include at least one longitudinally-extending tonguedisposed on a lower side of the center element. Alongitudinally-extending groove may be formed along an upper side of theupper element with the tongue and the groove of the center element beingoriented in perpendicular arrangement relative to one another. Acorresponding tongue may be formed on a lower side of the upper elementwith a corresponding groove being formed on an upper side of the lowerelement in order to slidably engage the corresponding tongue and grooveformed on the respective lower and upper sides of the center element.

In a preferable embodiment, the tongue and groove arrangements on theupper, center and lower elements are preferably provided with a dovetailconfiguration when viewed in transverse cross-section in order toprevent relative movement along a direction generally parallel to a postaxis (i.e., along a vertical axis of the post assembly).

Load transfer in the vertical direction between the tile and the postassembly may be facilitated through the use of at least one rope or acord element such as a cord fabricated of a suitable material such asNextel, Nomex, silica or fiberglass. It may be desirable to use multiplecords for each post assembly for increased vertical load transfercapability. The cord preferably extends substantially parallel to thepost axis and interconnects the tile to the post assembly and therebytransfers vertical loads. The cord preferably extends through a pair ofbores in the tile which are interconnected by a lateral groove formedjust beneath an upper side of the tile such that the cord forms aU-shaped loop, the lower ends of which may be bonded to the upperelement but the cords being unbonded to the tile or the strain isolationpad. In a further embodiment, the cord may be formed as a single strandextending through a single bore in the tile with the cord being bondedto the tile and the upper element such that the strain isolation padallows the tile to be at least partially free-floating relative to theupper element.

Angular alignment (i.e., clocking) of the tile to the post assembly maybe facilitated through the use of a pair of prongs extending upwardlyfrom an upper side of the upper element. A corresponding pair ofcounterbores may be formed in the lower surface of the tile to receivethe prongs. For embodiments of the attachment system that include theSIP, the prongs may extend through a complimentary set of aperturesformed therein. Clocking of the tile relative to the post assembly maybe desirable for configurations where the post assembly includes anouter geometry that must be aligned with the vehicle for certainpurposes such as for reduced radar reflectivity. The prongs may alsofacilitate lateral load transfer between the post assembly and the tile.

Regarding the connection between the upper element and the tile, a cordmay extend through a single bore or through a pair of bores formed inthe tile and through bores formed in the SIP and the upper element. Thecord in looped arrangement may be left unbonded to the tile although thelower ends of the looped cord may be bonded to a pair of bore formed inthe upper element. If provided as a single strand, the cord may bebonded to the tile via the use of an appropriate potting compound suchas a ceramic slurry or other suitable adhesive or potting compound. Thepotting compound may be fired at an appropriate elevated temperature.Following curing of the potting compound, the SIP and the upper elementmay be slipped over the cord.

The cord(s) may then be tensioned and a suitable potting compound may beinstalled in the annular gap between the cord and the upper element. Thepotting compound between the upper element and the cord may be amicroballoon-filled resin which may be oven-cured while the cord isunder tension such that the SIP is snugly sandwiched between the upperelement and the tile. After curing, an excess portion of the cord(s)extending out of the upper element may then be trimmed such that thecord(s) terminates inward of the lower side of the upper element toavoid interfering with the free sliding of the tongue of the lowerelement inside the groove of the center element.

The prongs of the upper element (which extend into the counterbores ofthe tile) may facilitate lateral load transfer between the tile and thepost assembly while the cord may facilitate vertical load transferbetween the tile and the post assembly. Following assembly of the upperelement to the tile, the center element may be slidably engaged to theupper element and the center element may be slidably engaged to thelower element. The lower element may then be bonded to the substructureusing an appropriate film adhesive.

The advantages provided by the attachment system as disclosed aboveinclude the ability to rapidly install and remove TPS from an air orspace vehicle or other vehicle for inspection, maintenance and repair ofthe substructure and/or subsystems underlying the TPS. A furtheradvantage provided by the attachment system includes the ability torapidly inspect, repair and replace tiles that may be damaged.

The mounting of the tile in spaced relation to the substructure via thepost assembly also facilitates the flow of cooling air through thecooling gap that is provided therebetween. The cooling gap improvescooling capacity and permits operation of the vehicle at much highertemperatures. Furthermore, the cooling gap may permit the use of lowercost and lower temperature epoxy composite structures as a substitutefor the relatively expensive polyimide structures required in vehiclesusing prior art attachment systems. In this regard, the attachmentsystem provides a survivable solution for controlling extremetemperatures generated by high thrust or afterburning engines.

The features, functions and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawingsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present disclosure will become moreapparent upon reference to the drawings wherein like numbers refer tolike parts throughout and wherein:

FIG. 1 is a diagram illustrating an attachment system in accordance withan advantageous embodiment;

FIG. 2 is a plan view of the attachment system in one embodimentcomprising a plurality of adjacently disposed tiles removeably mountedto a vehicle substructure utilizing a plurality of post assemblies;

FIG. 3 is a sectional illustration taken along line 3-3 of FIG. 2 andillustrating the mounting of the tiles in spaced relation to thesubstructure of the vehicle utilizing the plurality of post assemblies;

FIG. 4 is a sectional view illustrating the engagement of one of thetiles to the substructure by engagement of upper and center elementsmounted to the tile to corresponding lower elements mounted to thesubstructure;

FIG. 5 is a perspective cutaway view of one of the post assembliesillustrating the engagement of a center element of the post assembly tothe lower element mounted to the substructure;

FIG. 6 is a perspective cutaway illustration of the tile slidablyengaged to the substructure via the post assembly;

FIG. 7 is an exploded illustration of the TPS illustrating theinterconnectivity of the post assembly, a strain isolation pad (SIP) anda cord;

FIG. 8 is a partial cross-sectional illustration of the tileillustrating the bonding of the cord to a bore formed in the tile andillustrating a pair of counterbores formed in a lower surface of thetile;

FIG. 9 is a sectional illustration of the tile and the upper element ofthe post assembly wherein a pair of prongs are engaged to the pair ofcounterbores formed in the lower surface of the tile;

FIG. 10 is a sectional illustration of the tile mechanically attached tothe substructure via the post assembly and illustrating the SIPinstalled between the upper element of the post assembly and the lowersurface of the tile;

FIG. 11 is a sectional illustration taken along line 11-11 of FIG. 10and illustrating a cross section of the attachment system in a directiontransverse to the sectional illustration of FIG. 10.

FIG. 12 is a perspective illustration of the tile mechanically attachedto the substructure utilizing the post assembly having a cylindricalconfiguration;

FIG. 13 is an exploded perspective illustration of the cylindricallyshaped post assembly and illustrating a first sliding direction orientedin perpendicular relationship to a second sliding direction of the postassembly;

FIG. 14 is a sectional illustration of a cylindrically configured postassembly;

FIG. 15 is a flow chart of an exemplary process for fabricating theattachment system; and

FIG. 16 is a flow chart of an exemplary process for removing the tilefrom the substructure.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating preferred and various embodiments of the disclosure onlyand not for purposes of limiting the same, FIG. 1 is a diagramillustrating a mechanical attachment system 10 for mounting at least onetile 14 such as a tile 14 of a thermal protection system 12 (TPS) to avehicle 70 substructure 72 in accordance with an advantageousembodiment. The attachment system 10 may include at least one postassembly 36 for removably mounting at least one tile 14 in spacedrelation to the vehicle 70 substructure 72 such that a cooling gap 64may be formed between the tile 14 and the substructure 72. The coolinggap 64 may provide a channel for the flow of cooling air therebetween inorder to improve cooling capacity and/or to increase the temperatures atwhich the vehicle 70 substructure 72 may operate. The post assembly 36may be configured to facilitate sliding movement of the tile 14 relativeto the vehicle 70 substructure 72 along a plane that may be orientedgenerally parallel to the tile 14. The sliding movement of the tile 14relative to the substructure 72 may improve the mechanical attachmenttherebetween.

The vehicle 70 may be, without limitation, any type of vehicle includingan air vehicle such as an aircraft intended for atmospheric flight or ahypersonic vehicle or a space vehicle such as a reusable launch vehicle(RLV) or a crew exploration vehicle (CEV). Other vehicles 70 utilizingthe attachment system 10 may include, without limitation, vehicleshaving advanced air-breathing stages as well as supersonic air launchplatforms combining air-breathing and rocket stages for transatmosphericor orbital missions. However, the vehicle 70 may also comprise, withoutlimitation, any air vehicle, space vehicle, land vehicle, stationarystructure or immovable object such as a building structure or stationaryapparatus such as machinery.

In one embodiment, the tile 14 may be applied to portions of an airvehicle that are downstream of high temperature exhaust such as jetengine exhaust or rocket engine exhaust. In another embodiment, the tile14 may be applied to portions of a vehicle that may be capable ofwithstanding high operating temperatures as may be induced byatmospheric heating or radiative heating. The tile 14 may also beconfigured as a non-TPS element wherein relative movement between thetile 14 and the substructure 72 is desirable. For example, the tile 14may be configured as a panel element for any application whereinrelative movement between the tile 14 and the substructure 72 is desiredand wherein the tile 14 may be easily removed and replaced orreinstalled such as for inspection, repair, and/or replacement of thetile 14 or to facilitate inspection, repair and/or replacement of thesubstructure 72.

The post assembly 36 may be configured to facilitate relative slidingmovement between the tile 14 and the substructure 72 in one or moresliding directions. The sliding directions may be generally parallel toa plane defined by the tile 14 and/or by the substructure 72. In anexemplary embodiment, the post assembly 36 may be configured tofacilitate sliding movement in first and second sliding directions B, Cwherein the first sliding direction B is preferably, but optionally,oriented perpendicular to the second sliding direction C. However, thepost assembly 36 may be configured to facilitate relative movement insliding directions that may be oriented in non-perpendicularrelationship to one another.

The attachment system 10 may optionally include a strain isolation pad22 (SIP) which may be disposed between the post assembly 36 and the tile14. The SIP 22 may be configured to facilitate slight vertical and/orhorizontal movement of the tile 14 relative to the substructure 72without compromising the strength of the joint therebetween. Forexample, the SIP 22 may facilitate slight vertical movement of the tile14 relative to the substructure 72. In this regard, the SIP 22 may beconfigured to isolate the tile 14 from structural deflections of thevehicle 70 such as may occur under static and/or dynamic loading suchas, without limitation, a result of air frame-induced load deformations.In addition, the SIP 22 may be configured to isolate the tile 14 fromrelative movement as a result of thermal expansion and/or acousticexcitation in order to prevent stress failure in the tile 14.

The SIP 22 may be comprised of any suitable material and may be formedof felt-like material preferably having high-temperature operationalcapabilities. For example, in one embodiment, the SIP 22 may befabricated of Nextel ceramic fiber pad material or any other suitableflexible material that facilitates movement of the tile 14 relative tothe substructure 72 without compromising the strength of the jointtherebetween.

The post assembly 36 may comprise one or more elements which may beconfigured to facilitate the relative sliding movement between the tile14 and the substructure 72. For example, in one embodiment, the postassembly 36 may comprise a lower element 44, a center element 42 and anupper element 40 although the post assembly 36 may comprise any numberof elements. The lower element 44 may be fixedly mounted to thesubstructure 72 such as by bonding with a suitable adhesive and/or bymechanically connecting the lower element 44 to the substructure 72.

The center element 42 may be slidably engageable to the lower element 44such that the center element 42 may move relative to the lower element44 along a direction that is generally parallel to the tile 14 and/orthe substructure 72. In one embodiment, the center element 42 may beconfigured to be slidable relative to the lower element 44 along thefirst sliding direction B. The center element 42 may also be slidablyengageable to the lower element 44 such that relative vertical movementtherebetween is prevented.

The upper element 40 may be fixedly mountable to the SIP 22. However,the upper element 40 may optionally be fixedly mountable directly to thetile 14 if the SIP 22 is omitted from the attachment system 10. Theupper element 40 is preferably configured to be slidably engageable tothe center element 42. In one embodiment, the upper element 40 may beconfigured to be slidable relative to the center element 42 along thesecond sliding direction C. The upper element 40 may also be slidablyengageable to the center element 42 such that relative vertical movementtherebetween is prevented.

The attachment system 10 may include an interlocking mechanism 46between any one of the adjacently-disposed elements. For example, aninterlocking mechanism 46 may be provided between the lower element 44and the center element 42. Likewise, an interlocking mechanism 46 may beprovided between the center element 42 and the upper element 40. Theinterlocking mechanism 46 may be configured to facilitate slidableengagement of adjacently-disposed elements with one another.Furthermore, the interlocking mechanism 46 may facilitate relativesliding movement between adjacently-disposed elements such as betweenthe lower element 44 and the center element 42 and between the centerelement 42 and the upper element 40.

In an advantageous embodiment, the interlocking mechanism 46 maycomprise a longitudinally-extending tongue 42 c disposed on the centerelement 42 and a longitudinally-extending mating groove 44 d disposed onthe lower element 44. Likewise, a longitudinally-extending tongue 40 cmay be disposed on the upper element 40 and a longitudinally-extendingmating groove 42 d disposed on the center element 42. The tongues 40 c,42 c and respective grooves 42 d, 44 d may be configured to be slidablyengageable to one another.

The attachment system 10 may include at least one rope or cord 32extending between the post assembly 36 and the tile 14 as a means tofacilitate vertical load transfer therebetween. The cord 32 may beoriented substantially perpendicularly relative to the tile 14 and maybe mechanically attached to the tile 14 without adhesive although thecord 32 may be bonded to the tile 14 and/or post assembly 36. The cord32 may be bonded to a bore 26 formed in the tile 14. The cord 32 mayextend through the SIP 22 which may be captured between the postassembly 36 and the tile 14. In this regard, the SIP 22 allows the tile14 to be at least partially free-floating relative to the upper element40 while allowing the cord 32 to transfer vertical loads between thesubstructure 72 and the tile 14.

The upper element 40 may include at least one prong 38 extendingupwardly therefrom and being engageable to the tile 14. In anadvantageous embodiment, a pair of prongs 38 may be provided and mayengage a corresponding pair of counterbores 20 optionally formed in thetile 14 to facilitate angular alignment of the tile 14 to the postassembly 36. The prongs 38 may also be configured to facilitate lateralload transfer between the tile 14 and the post assembly 36 while thecord 32 may facilitate vertical load transfer between the tile 14 andthe post assembly 36 as described above.

FIG. 2 is an illustration in plan view of a thermal protection system(TPS) 12 comprising a plurality of tiles 14 mounted to a vehicle 70.More specifically, FIG. 2 illustrates an arrangement of tiles 14 mountedto the substructure 72 such as of an air vehicle or a space vehicle.FIG. 2 also illustrates a plurality of attachment systems 10 formounting the tiles 14 to the substructure 72 wherein the attachmentsystems 10, in one embodiment, may comprise at least one post assembly36 configured to secure at least one tile 14 to the substructure 72.

As shown in FIG. 2, a plurality of the post assemblies 36 may beemployed to mount a single one of the tiles 14 to the vehicle 70substructure 72. However, any number of the post assemblies 36 includinga single one of the post assemblies 36 may be utilized for mounting thetile 14 to the substructure 72. In this regard, the tile 14 may comprisea variety of different components including, but not limited to, anythermal protection system 12 to be removably mounted to the substructure72.

The tiles 14 may comprise rigid, flexible and/or semi-flexible tiles 14which may be fabricated of a variety of materials. For example, thetiles 14 may comprise ceramic tiles 14 for use on a reusable launchvehicle (RLV). Furthermore, the post assembly 36 may be employed forattaching any type of structure other than TPS 12 elements to thesubstructure 72. For example, the post assembly 36 may be employed forslidably securing various system components to the substructure 72wherein lateral movement (i.e., movement along or parallel to the planeof the substructure 72) is desired.

Referring to FIGS. 2-4, the tiles 14 are shown as having a generallyorthogonal or rectangular shape although the tiles 14 may be provided inany shape, size and configuration. In addition, FIGS. 2-3 show the tiles14 as being generally disposed in slightly spaced relationship such thata gap 50 may be formed between adjacently disposed tiles 14. The gap 50between the tiles may facilitate thermal expansion or contraction of thesubstructure 72. As such, the tiles 14 may be provided or arranged inslightly spaced relationship relative to one another to preventtile-to-tile 14 contact therebetween during thermal expansion orcontraction of the substructure 72.

The side-to-side gap 50 allowance between the tiles 14 may alsocompensate for assembly tolerances of the tiles 14 relative to thesubstructure 72 and/or machining tolerances of the tiles 14. Each of thegaps 50 between the adjacent tiles 14 is preferably filled with a TPSseal 24 which may be formed of a suitable material such as Nextelpadding or other filler bar materials to facilitate waterproofing andtemperature resistance but allowing relative movement between the tiles14 as may occur during the dynamic loading conditions of vehicle flight.

Regarding the spacing of the post assemblies 36, FIG. 2 illustrates aspacing of approximately 4 inches to 6 inches on centers betweenadjacent post assemblies 36 for an exemplary 2 foot by 2 foot tile 14.However, it should be noted that spacings of the post assemblies 36 maybe provided in any suitable arrangement in order to secure the tile 14assembly to the substructure 72 while allowing little relative axialmovement between the supported portions of the tile 14 and thesubstructure 72.

Referring particularly now to FIGS. 3 and 4, shown is the thermalprotection system 12 wherein the tiles 14 are disposed in spacedrelationship to the substructure skin 74. In this regard, the postassemblies 36 advantageously facilitate the flow of cooling air betweenthe tile 14 and the substructure 72 as may be desirable on certainapplications in order to improve cooling capacity and permit operationat much higher temperatures. In this regard, FIG. 3 illustrates hot flowover an upper surface 16 of the tile 14 and cooling flow passing betweenthe lower surface 18 of the tile 14 and the substructure skin 74.

Importantly, the post assembly 36 is specifically configured to allowrelative sliding movement between the tile 14 and the substructure 72along a plane which is generally parallel to the tile 14 upper and/orlower surfaces 16, 18. As can be seen in FIG. 4, shown is the tile 14 ina removed position relative to the substructure skin 74 as may bedesired for inspection, access and maintenance to the substructure 72and/or subsystems below the tile 14 and for inspection and orreplacement of the tiles 14 themselves should the tiles 14 becomedamaged. The post assemblies 36 are shown disengaged from thesubstructure 72 with the arrows in FIG. 3 illustrating a direction alongwhich the post assembly 36 may be re-engaged.

Referring to FIG. 7, the post assembly 36 may be configured to allowrelative movement between the tile 14 and the substructure 72 in atleast one of first and second sliding directions B, C. As indicatedabove, the first sliding direction B may be oriented generallyperpendicularly relative to the second sliding direction C as best seenin FIG. 7. However, the post assembly 36 may be configured to facilitaterelative movement in only a single sliding direction or in three or moresliding directions. Furthermore, the first and second sliding directionsB, C may be oriented in non-perpendicular relationship to one another.

Referring to FIGS. 3-4, the cooling gap 64 between the tiles 14 and thesubstructure 72 and, more particularly, between the lower surface 18 ofthe tile 14 and the substructure skin 74 is desirable in order topromote cooling flow therebetween. In particular, the cooling gap 64between the tiles 14 and the substructure 72 is desirable in areas thatare subject to high heat for prolonged periods of time such as directlybehind an engine wherein the tiles 14 are subject to sustainedimpingement by the exhaust plume of an air breathing engine or a rocketengine. In this regard, the spaced relationship between the tile 14 andthe substructure 72 as illustrated in FIGS. 3-4 facilitates cooling airflow which, in one example, can be passively generated or can beactively provided by pumping air from a compressor of a jet engine.

In addition, air may be forced through into the cooling gap 64 throughthe use of ejectors which direct air from a high pressure region of theaircraft/spacecraft into the cooling gap 64 between the tile 14 and thesubstructure 72. The cooling gap 64 between the tiles 14 and thesubstructure 72 permits the use of lower cost and lower temperatureepoxy composite structures rather than the more expensive polyimidestructures typically used in prior art structures wherein the TPS 12 isdirectly bonded to the substructure.

Referring now to FIGS. 5-7, shown is a partial cutaway view of the tile14 illustrating the interconnectivity thereof to the post assembly 36.The post assembly 36 may be comprised of a lower element 44, a centerelement 42, and an upper element 40. The lower element 44 can be seen asbeing fixedly mountable to the substructure 72 of the vehicle 70. Thecenter element 42 is preferably slidably engageable to the lower element44. The upper element 40 is preferably fixedly mountable to the tile 14and is slidably engageable to the center element 42.

Importantly, the upper element 40 is slidable relative to the centerelement 42 along the first sliding direction B. The center element 42 ispreferably slidable relative to the lower element 44 along the secondsliding direction C. In the exemplary embodiments illustrated in FIGS.2-4, the first sliding direction B may be in alignment with theinboard/outboard direction of the vehicle 70. The second slidingdirection C may preferably be generally oriented in alignment with thefore/aft direction of the vehicle 70.

In the exemplary embodiments of the attachment system 10 illustrated inFIGS. 2-11, the post assembly 36 may have a diamond shaped cross-sectionwhen the post assembly 36 is viewed along a post axis indicated byreference character A. The diamond shaped configuration of the postassembly 36 is a preferred embodiment and may facilitate a reduction inradar signature and an increase in load transfer capability as comparedto a cylindrical configuration of the post assembly 36 shown in FIGS.12-14 and as described in greater detail below. The diamond shapedconfiguration may therefore allow for a reduced cooling gap 64 betweentile 14 and substructure 72. In addition, the diamond-shaped postassembly 36 may be tapered to a reduced cross-section from the lowerelement 44 toward the upper element 40. However, it should be noted thatthe post assembly 36 may be provided in any suitable size, shape andconfiguration other than the diamond shaped or cylindrically shapedconfigurations.

Referring to FIGS. 7-11, shown is the post assembly 36 which maycomprise the lower element 44, the center element 42 and the upperelement 40. The lower element 44 may preferably be bonded to thesubstructure 72 using any suitable adhesive 62 such as, withoutlimitation, FM-680-1 film adhesive, commercially available from CytecIndustries Inc., West Patterson, N.J. However, other suitable adhesivesmay be used. Furthermore, it is contemplated that, in addition to or inconjunction with adhesives, the lower element 44 may be mechanicallyfastened to the substructure 72 using any suitable mechanical fasteningtechnology.

As can be seen in FIG. 5, the lower element 44 comprises a slightlytapered configuration having a diamond shaped profile when viewed alongthe post axis A. In a preferable embodiment, the lower element 44 isflat or slightly curved complementary to the substructure 72 in order tofacilitate a good adhesive bond between the lower side 44 b of the lowerelement 44 and the substructure skin 74. In this regard, the attachmentsystem 10 as described herein is preferably adapted for use on generallyflat or planar surfaces or slightly curved surfaces although it iscontemplated that the attachment system 10 may be applied to curvedinstallations such as, without limitation, complex curved geometries.

It is also further contemplated that for installation of a large numberof tiles 14 over a relatively large area, at least one of the tiles 14may have a unique attachment mechanism that permits installation of thetile 14 without sliding into position and thereby prevents shifting ofthe installed tiles during use such as may occur as the result of staticor dynamic loading. In this regard, shifting of the other tiles 14 maybe prevented by the installation of a tile 14 that is installablewithout sliding into position. In this manner, a matrix of tiles 14 maybe installed by first installing tiles 14 having the attachment system10 described above followed by installing a single remaining tile 14that may be locked into position with a non-sliding or otherwise uniqueattachment mechanism. In such an arrangement and for situations where adamaged tile 14 must be removed, the tile 14 with the unique attachmentmechanism must be removed first prior to slidably disengaging theremaining tiles 14 from the substructure 72.

Referring to FIGS. 5-7, the attachment system 10 may include the centerelement 42 which is preferably provided with at least one interlockingmechanism 46. Importantly, the interlocking mechanism 46 is configuredto allow sliding movement of the center element 42 relative to the upperand/or lower elements 40, 44 along at least one of the first and secondsliding directions B, C. For example, as shown in FIG. 7, the centerelement 42 may include a groove 42 d formed on an upper side 42 athereof with a tongue 44 c being formed on a lower side 42 b of thecenter element 42. Likewise, a corresponding groove 44 d may be formedon an upper side 44 a of the lower element 44 and a corresponding tongue40 c may be formed on the lower side 40 b of the upper element 40.

The interlocking mechanism 46 (illustrated for exemplary purposes as thetongue and groove configuration) facilitates relative movement along thefirst and second sliding directions B, C which can be seen as beingoriented generally perpendicular relative to one another. Furthermore,the tongue and groove configurations are sized and configured to providea preferable non-interference fit at elevated operating temperatures.Importantly, the attachment system 10 facilitates sliding movement atsuch elevated operating temperatures to prevent failure of the joint dueto binding as a result of thermal movement.

Referring briefly to FIGS. 10 and 11, the interlocking mechanism 46 maybe configured to prevent movement along a direction that is generallyparallel to the post axis A (i.e., in the vertical direction). In thisregard, the tongues 40 c, 42 c and the grooves 42 d, 44 d may be taperedinto a dovetail configuration when viewed along a transversecross-section. The dovetail configuration may prevent movement of thetile 14 in the axial direction (i.e., along the post axis A). It shouldalso be noted that although the interlocking mechanism 46 is illustratedas being configured in the tongue and groove arrangement, theinterlocking mechanism 46 may be provided in any variety of shapes,sizes and alternative configurations.

For example, it is contemplated that the interlocking mechanism 46 maycomprise a lip element (not shown) which is configured to engage acomplimentary shaped slot element (not shown) formed in any one of thelower, center and upper elements, 44, 42, 40. Furthermore, although theillustrated exemplary embodiments show the center element 42 as having agroove 42 d on an upper side 42 a thereof and a tongue 42 c on a lowerside 42 b thereof, the center element 42 may be provided with a tongueformed on the upper side 42 a and a groove formed on the lower side 42 bto engage a complimentary shaped tongue and groove on the lower andupper elements 44, 40, respectively. Regardless of the specificconfiguration of the interlocking mechanism 46, the lower, center andupper elements, 44, 42, 40 are preferably configured to facilitatesliding movement along at least one of the first and sliding directionsB, C while preventing relative movement along a direction parallel tothe post axis A.

Referring to FIGS. 7-11, shown is the upper element 40 having at leastone and, more preferably, a pair of prongs 38 extending upwardly from anupper side 40 a of the upper element 40. The prongs 38 are preferablyconfigured to extend into a matching set of counterbores 20 formed in anunderside of the tile 14 as best seen in FIGS. 7 and 10. The prongs 38are preferably provided in order to facilitate clocking alignment of thetile 14 relative to the upper element 40 and to facilitate lateral loadtransfer between the post assembly 36 and the tile 14. It should also benoted that although the upper element 40 is provided with a pair ofprongs 38, any suitable feature having any configuration may be providedon the upper element 40 in order to facilitate alignment of the tile 14with the upper element 40 and to facilitate lateral load transferbetween the post assembly 36 and the tile 14 (i.e., generally along aplane that is parallel to the tile 14). In this regard, the lateral loadtransferring capability provided by the prongs 38 limits or preventslateral or sideways movement of the tile 14 relative to the postassembly 36 under static or dynamic forces imposed on the tile 14 suchas may occur during high-speed atmospheric flight.

Referring to FIGS. 9-11, the attachment system 10 preferably includesthe strain isolation pad 22 (SIP) which is preferably interposed betweenthe tile 14 and the post assembly 36. The SIP 22 is advantageouslyprovided in order to facilitate relative movement between the tile 14and substructure 72 as a result of air frame load-induced deformations.In this regard, the SIP 22 facilitates stress isolation of the tiles 14in response to structural deflections, expansions and acousticexcitations and thereby prevents undesirable stresses in the tiles 14 asmay otherwise occur without the attenuating effects of the SIP 22 inresponse to direct transfer of vertical loads between the tiles 14 andthe substructure 72. In a preferred embodiment, the SIP 22 may besandwiched between the upper element 40 and the lower surface 18 of thetile 14. However, it is contemplated that in certain embodiments it maybe desirable to bond the SIP 22 to the upper element 40 using a suitablefilm adhesive. Likewise, the SIP 22 may be bonded to the lower surface18 of the tile 14.

Vertical load transfer between the tile 14 and the post assembly 36 maybe facilitated by at least one cord 32 which may extend substantiallyparallel to the post axis A and which interconnects the tile 14 to thepost assembly 36 as shown in FIG. 7. The cord 32 is preferablyconfigured to facilitate load transfer from the upper element 40 to thelower surface 18 of the tile 14. In this regard, the cord 32 may bebonded to the tile 14 wherein the cord 32 is inserted into a bore 26formed through a thickness of the tile 14 as best seen in FIG. 7. In apreferable arrangement, the cord 32 may be provided in a invertedU-shaped loop extending through a pair of side-by-side bores 26 formedin the tile 14 and interconnected by a lateral groove (not shown) formedbeneath an upper surface 16 of the tile 14. The lateral groove may be ofa size and depth such that the cord 32 may nest therewithin. A plug (notshown) may optionally be installed such as by press-fitting into theupper surface 16 of the tile 14 with a lower end of the plug beingplaced in bearing contact with the cord 32 lying in the lateral grooveto clamp the cord 32 therebetween with no adhesive being used to bondthe cord 32 to the tile 14. The plug may be configured to lie flush withthe upper surface 16 of the tile 14 such that an upper skin may be laidthereover. The lower ends of the U-shaped cord 32 may be secured to theupper element 40 such as by bonding.

The cord 32 may be fabricated of any suitable temperature-resistantmaterial such as ceramic material. For example, the cord 32 may befabricated of, without limitation, Nextel, silica, Nomex, or fiberglassrope or from other suitable materials appropriate for the temperaturesat the location. The cord 32 may be potted into the tile 14 using aceramic potting compound 30 such as a ceramic slurry. The pottingcompound 30 may be any suitable compound capable of high temperatureenvironments. For example, the potting compound 30 may comprise ceramicpotting. Upon insertion of the cord 32 into the bore 26 of the tile 14and installation of potting compound 30, the potting compound 30 may befired such as in an oven at the appropriate temperature in order toallow the potting compound 30 to bond the cord 32 to the tile 14.

The cord(s) 32 may be secured to the upper element 40 using a suitablepotting compound 30 inserted into the annular space between the cord 32and the bore 26 in the upper element. In this regard, a suitablepolyimide potting compound 30 resin may be inserted between the cord 32and the upper element 40 bore. The polyimide potting compound 30 resinmay comprise, without limitation, AFR-PE4 microballoon-filled resin,commercially available from Maverick Corporation, Blue Ash, Ohio.Although the cord 32 is bonded to the upper element, the SIP 22 ispreferably not bonded to the cord 32 in order to facilitate freemovement between the upper element 40 and the ceramic tile 14 as mayoccur during acoustic excitation of the tile 14.

Referring briefly to FIGS. 12-14, shown is the post assembly 36 in acylindrical configuration. In the arrangement shown, the lower element44, center element 42 and upper element 40 may be provided with acircular cross-section when viewed along the post axis A. As can be seenin FIG. 14, the spacing or cooling gap 64 between the tile 14 and thesubstructure 72 is relatively large as compared to the cooling gap 64for the diamond shaped post assembly 36.

In addition, the cylindrically shaped lower element 44 may be providedwith a flange 52 for greater surface area as best seen in FIGS. 12 and13 to facilitate bonding to the substructure skin 74 with film adhesive.The upper element 40 may optionally be devoid of alignment features suchas the prongs 38 illustrated in FIG. 7 although alignment features canbe provided in multiples shapes and configurations in the cylindricalpost assembly 36. In this regard, the cylindrical configuration of thepost assembly 36 may be recessed into the tile 14 for transferringlateral loads between the tile 14 and the upper element 40 due to lackof such alignment features which can preferably be incorporated. Inaddition, recessing of the cylindrical configuration of the postassembly 36 into the tile 14 may facilitate positioning of the tile 14relative to the post assembly 36. The addition of alignment features inthe upper element 40 may facilitate clocking orientation of the tile 14relative to the post assembly 36. Referring still to FIGS. 12-14, thelower, center and upper elements 44, 42, 40 may be provided withsuitable interlocking mechanisms 46 such as the tongue and groovearrangement similar to that which is shown in FIGS. 5-11 for the diamondshaped post assembly 36.

Referring to FIGS. 8-11 and 15, a method of fabricating the attachmentsystem 10 will now be described. As was indicated above, the attachmentsystem 10 may be used for slidably mounting the tile 14 to a vehicle 70.The method may comprise step 100 of providing an SIP 22 and the upperelement 40. The upper element 40 may preferably have at least onealignment feature such as the pair of cylindrically shaped prongs 38extending upwardly from an upper side 40 a of the upper element 40.

The pair of apertures 28 may be formed in the SIP 22 in step 106. Theprongs 38 may be extended through the apertures 28 and may engage thecomplimentary shaped pair of counterbores 20 formed in the lower surface18 of the tile 14 in step 104. The counterbores 20 are preferablycylindrically shaped in order to match the general cylindrical shape ofthe prongs 38. However, it should be noted that the alignment featuremay be provided in a variety of alternative shapes, sizes andconfigurations other than the cylindrical shaped prongs 38 illustratedin the figures. The tile 14 may include a bore 26 which may be formed asa pair of bores 26 in step 102. The bore 26 in the tile 14 is preferablyco-axially aligned with and sized complimentary to the bore 26 formed inthe SIP 22 and the upper element 40.

In one embodiment of the assembly process, the cord 32 may be insertedinto the bore 26 in step 108. The cord 32 may be of a smaller diameterthan the bore 26 such that an annular gap may be provided between thebore 26 and the cord 32 to facilitate the insertion of the pottingcompound 30 for bonding the cord to the tile 14 in step 110. However,the cord 32 may be unbonded to the tile 14 using mechanical means (e.g.,a plug) to clamp the cord 32 to the tile 14. The potting compound 30 maybe installed and may be oven cured. Preferably, the cord 32 extendsthrough the thickness of the tile 14 with an excess portion 34 of thecord 32 extending from the lower surface 18 of the tile 14 as best seenin FIG. 8. The SIP 22 and the upper element 40 may then be installedover the cord 32 in step 112 such that the cord 32 extends through thebores 26 formed in the SIP 22 and upper element. In step 112, the upperelement 40 may be engaged against the SIP 22 and tile 14 such that theprongs 38 extend into the counterbores 20 formed in the lower surface 18of the tile 14 as best seen in FIG. 9.

In step 114, tension is then applied to the cord 32 while the upperelement 40 and the SIP 22 are forced against the tile 14 during bondingof the cord 32 to the upper element 40 with potting compound 30 in step116. The potting compound 30 may be any suitable compound such aspolyimide potting compound. Following curing (e.g., oven curing) of thepotting compound 30 and the cord 32 may be placed under tension, theexcess portion 34 may be trimmed in step 118 such that the cord 32 mayterminate at an inward portion 64 of the lower side of the upper element40.

In this regard, the free end of the cord 32 is preferably recessed intothe upper element 40 in order to prevent interference with the slidingof the tongue 40 c in the groove 42 d of the center element 42.Following curing of the potting compound 30 and trimming of the excessportion 34 as shown in FIG. 9, the upper element 40 and tile 14 may beslidably engaged onto the center element 42 in step 120 such that theupper element 40 is slidable along the first sliding direction B but isnon-movably fixed in a direction along the post axis A.

Likewise, the lower element 44 may then be slidably engaged onto thecenter element 42 in step 122 such that the center element 42 isslidable along the second sliding direction C as best seen in FIG. 7.Preferably, the interlocking mechanisms 46 formed on the upper, centerand lower elements, 40, 42, 44 are such that relative movement in theaxial direction (i.e., along the post axis A) is prevented. Followingassembly of the post assembly 36, the lower element 44 may then bebonded to the substructure 72 in step 124 using a suitable adhesive 62such as polyimide film adhesive.

Referring to FIGS. 5-7 and 16, a method of removing and installing atile that is mounted to a vehicle substructure will now be described. Aswas earlier mentioned, it may be desirable to remove a tile 14 for avariety or reasons such as, for example, the case wherein the tile 14 isdamaged and requires installation of a replacement tile 14. Furthermore,the tile 14 may require removal for the case wherein the inspection ofthe tile 14 and/or the substructure 72 is desired.

In step 130, tile 14 may be removed from the vehicle 70 substructure 72by either slidably disengaging the upper element 40 from the centerelement 42 along the first sliding direction B such that the tile 14 andupper element 40 are removed as a unit leaving the lower element 44fixedly mounted to the substructure 72, or, by slidably disengaging thecenter element 42 from the lower element 44 along the second slidingdirection C such that the tile 14, upper element 40 and center element42 are removed as a unit leaving the lower and center elements 44, 42mounted to the substructure 72. Optionally, if an SIP 22 is providedbetween the tile 14 and the upper element 40, the SIP 22 will also beremoved with the tile 14 as a unit.

Following removal of the tile 14, step 132 includes reinstalling thetile 14 as a unit. Alternatively, a tile 14 replacement may be providedwherein the tile 14 may include the upper element 40 which may befixedly mounted thereto or the tile 14 may include both the upperelement 40 and the center element 42 as appropriate depending uponwhether the substructure 72 has a lower element 44 mounted thereon orthe substructure 72 has both lower and center elements 44, 42 mountedthereon.

In step 134, the tile 14 may be installed by slidably engaging the upperelement 40 to the center element 42 along the first sliding direction B,or, by slidably engaging the center element 42 to the lower element 44along the second sliding direction C. As shown in FIG. 2, the tile 14may include a plurality of post assemblies 36 such that removal andinstallation of the tile 14 may require slidable engagement of each ofthe upper elements 40 to the respective center elements 42 and/orslidable engagement of each of the center elements 42 to the respectivelower elements 44 such that the upper, center and lower elements 40, 42,44 of all the post assemblies 36 are slidably engaged to one another asshown in FIG. 3.

As was mentioned above, the interlocking mechanisms 46 which facilitatesliding engagement of the lower, center and upper elements 44, 42, 40preferably comprise at least one of a longitudinally extending tongue 44c or a longitudinally extending groove 44 d on the upper side 44 a ofthe lower element 44. Likewise, a tongue 42 c and groove 42 d arepreferably formed on opposing upper and lower sides 42 a, 42 b, of thecenter element 42 and a longitudinally extending tongue 40 c on thelower side 40 b of the upper element 40.

Following curing of the film adhesive 62 between the lower element 44and the substructure skin 74, the tongue and groove features formed withthe post assembly 36 facilitate sliding movement in at least one of thefirst and second sliding directions B, C as best seen in FIG. 7 for thediamond shape configuration and in FIG. 13 for the cylindrically shapedconfiguration of the post assembly 36. A preferable clearance betweenthe tongue 40 c, 42 c and groove 42 d, 44 d is within the range ofapproximately 0.002 inches to 0.003 inches although any range ofclearance between the tongue 40 c, 42 c and groove 42 d, 44 d of theupper, center and lower elements 40, 42, 44 of the post assembly 36 issuitable. The non-interference fit is preferably provided in order toprevent binding such as due to thermal expansion and/or structuralbending at extreme operating temperatures.

Regarding materials from which the attachment system 10 may befabricated, the upper element 40 may be fabricated frompolybenzimidazole which is commercially available as Celazole PBIavailable from Celanese Advanced Materials, Charlotte, N.C. The CelazolePBI material as used in the upper element 40 is a preferable materialdue to its high temperature stability, strength, chemical resistance andnon-flammability. The upper element 40 may be fabricated from suchmaterial using any suitable manufacturing process such as compressionmolding or injection molding. Likewise, the center element 42 may befabricated from Celazole PBI due to its high compressive strength atelevated temperatures, superior wear resistance and high dimensionalstability.

A preferable material from which the lower element 44 may be fabricatedincludes any suitable compression molded polyimide resin such asAFR-PE4. In this regard, AFR-PE4 is a suitable material when bonding toa polyimide substructure. AFR-PE4 has the capability to withstandlong-term exposure to extreme temperatures and is thermally matched tothe substructure 72 (i.e., compatible coefficient of thermal expansion)in order to minimize strain on the adhesive 62 bond joint. The postassembly 36 may also be fabricated of materials having favorabledielectric or radar reflectivity properties as may be desirable formilitary applications. However, it is contemplated that any metallicand/or non-metallic material or combination thereof may be used forfabricating the upper, center and lower elements 40, 42, 44 of the postassembly 36. The SIP 22 may be fabricated of any suitable flexiblematerial having high temperature properties. For example, Nextel ceramicfiber pad may be utilized for fabricating the SIP 22. The ceramic ropeor cord 32 may be fabricated likewise using Nextel or Nomex material.

The attachment system 10 as disclosed above provides a mechanism formechanically attaching tile 14 of a thermal protection system 12 to anexterior surface of a substructure 72 such as of an air vehicle, a spacevehicle or land-based vehicles and immobile structures and objects.Advantageously, the attachment system 10 facilitates quick and rapidinspection of installed tiles 14 and reduces maintenance touch labor andvehicle 70 downtime to repair and replace damaged tiles 14. In addition,the attachment system 10 provides a relatively large cooling channel orgap 64 between the lower surface 18 of the tile 14 and the substructureskin 74.

The cooling gap 64 improves cooling capacity and permits operation atmuch higher temperatures relative to prior art TPS installations whereinthe tiles 14 are bonded directly to the substructure 72. Finally, theattachment system 10 provides a means for cooling capacity in order tofacilitate use of lower cost and lower temperature epoxy compositestructures for the substructure 72 underneath the tiles 14 in lieu ofmore expensive polyimide structures.

Furthermore, the attachment system 10 as disclosed above permits removaland replacement of tiles 14 in a drastically reduced amount of time ascompared to the rather lengthy time period required for prior art directbonding of tiles 14. In addition, the attachment system 10 permitshigher propulsion exhaust temperatures over trailing structures due tocooling flow in the cooling gap 64 between the lower surface 18 of thetile 14 and the substructure skin 74. In this regard, the attachmentsystem 10 provides a survivable solution for controlling extremetemperatures exhibited at locations in the exhaust path of an airbreathing engine or rocket engine, particularly high thrust orafter-burning engines on next generation military aircraft.

Additional modifications and improvements of the present disclosure maybe apparent to those of ordinary skill in the art. Thus, the particularcombination of parts described and illustrated herein is intended torepresent only certain embodiments of the present disclosure and is notintended to serve as limitations of alternative embodiments or deviceswithin the spirit and scope of the disclosure.

1. A method of mounting a tile to a substructure, the method comprisingthe steps of: providing at least one element and a strain isolation pad;forming a bore in the tile, the at least one element, and the strainisolation pad; inserting a cord into the bore of the tile such that anexcess portion of the cord extends outwardly from the tile; bonding thecord to the tile; inserting the cord into the bore of the strainisolation pad and the at least one element such that the strainisolation pad is disposed between the tile and the at least one element;applying tension to the cord while the at least one element and thestrain isolation pad are forced against the tile; bonding the cord tothe at least one element while the cord is under tension; and bondingthe at least one element to the substructure.
 2. The method of claim 1wherein the step of forming the bore in the tile and the at least oneelement includes forming the bore coaxially in the tile and the at leastone element.
 3. The method of claim 1 wherein the at least one elementcomprises a lower element, a center element and an upper element.
 4. Themethod of claim 3 comprising the steps of: forming the bore in the tile,the upper element and the strain isolation pad; inserting the cord intothe bore of the strain isolation pad and the upper element such that thestrain isolation pad is disposed between the tile and the upper element;applying tension to the cord while the upper element and the strainisolation pad are forced against the tile; bonding the cord to the upperelement while the cord is under tension; and bonding the lower elementto the substructure.
 5. The method of claim 3 further comprising thesteps of: slidably engaging the center element onto the upper elementsuch that the upper element is slidable along a first sliding direction;and slidably engaging the lower element onto the center element suchthat the center element is slidable along a second sliding directiongenerally perpendicular to the first sliding direction.
 6. The method ofclaim 3 further comprising the step of: forming an interlockingmechanism on at least one of the lower, center and upper elements. 7.The method of claim 6 wherein the step of forming the interlockingmechanism comprises: forming at least one of a tongue and a groove on anupper side of the lower element; forming at least one of a tongue and agroove on each of opposing upper and lower sides of the center element;and forming at least one of a tongue and a groove on a lower side of theupper element; the interlocking mechanism being configured such that thetongue and groove formed on the upper and lower sides of the centerelement are slidably engageable to the corresponding tongue and grooveformed on the lower element and on the upper element; the tongue andgroove formed on the upper side extending along the first slidingdirection, the tongue and groove on the lower side extending along thesecond sliding direction.
 8. The method of claim 1 further comprising:forming at least one alignment feature on the element; and engaging thetile with the alignment feature.
 9. The method of claim 8 wherein thestep of forming at least one alignment feature on the element andengaging the tile with the alignment feature comprises forming a pair ofprongs on the element; forming a pair of counterbores in the tile; andengaging the prongs to the counterbores.
 10. The method of claim 1further comprising: trimming the cord such that the cord is recessedinto the element.
 11. A method of removing and installing a tile mountedto a substructure using an attachment system having a post assemblycomprising a lower element, a center element and an upper element, thelower element being fixedly mounted to the substructure, the centerelement being engaged to the lower element and being slidably movablealong a second sliding direction, the upper element being engaged to thecenter element and being slidably movable along a first slidingdirection, the method comprising the steps of: removing the tile fromthe substructure by performing at least one of the following: slidablydisengaging the upper element from the center element on an end of thecenter element opposite the tile and along the first sliding directionsuch that the tile and upper element are removed as a unit; slidablydisengaging the center element from the lower element along the secondsliding direction oriented generally parallel to a longitudinaldirection of the tile such that the tile, upper element and centerelement are removed as a unit; and providing a tile replacement havingat least one of an upper element and a center element mounted thereto;and mounting the tile replacement to the substructure by performing atleast one of the following: slidably engaging the upper element to thecenter element along the first sliding direction; slidably engaging thecenter element to the lower element along the second sliding direction.12. The method of claim 11 wherein the attachment system furtherincludes a cord interconnecting the tile to the upper element.